I could generate the images myself, if I had any interest in it, I could even draw them by hand or paint them in a number of means. The fact is my interest remains in writing, and I feel that to be both a waste of time something that would derail me for weeks from the purpose of publishing 10 minutes of written text. In this way, I rather use images that I feel are within the feeling I want to trasnmit with my text which are of freeuse and I get them down to the colors I want. If there are any that I really want that have some copyright, then I ask for permission from the authors.
In cases that need no special kind of Image, I have no problem in publishing my own pictures or creating some illustration, but, for the case that I am refering to, which is my space opera, it's just not feasable.
Thanks very much for your comment. :)